Preparation of iron aluminum alloys



2, 80 l:,38 7 PREPARATION or 'nroN ALUMINUM ALLOYS? Eric R. Morgan andVictor F. Zackay,D-arborn, Mich,

assignors to Ford Motor compan Dear-born, Mich, a corporation ofDelaware No Drawing; Application N ovember 14; .1955, SerialNo. 546,762'

3 Ciaim's; (Cl. 75 -124) This invention is in the field offerrous.metallurgy and is specifically directed to a process for the preparationof ductile iron aluminum alloys containing up to 18% aluminum.

Considerable scientific interest has been. generatedre cently in ironaluminum alloys containing up to 18% aluminum, because of theirexcellent magnetic and electrical properties and resistance to heat'andoxidation combined with their'very acceptable tensile properties atelevated temperatures. These qualities are obtainable despite thecomplete" absence of any of the so called critical or sensitive alloys.The commercial utilization of these iron aluminum alloyshasbeenhandicappedv by the necessity of preparing them in vacuum equipment.While this type of vacuum apparatus is practical and feasibleon a smallscale, it is to be avoided on a largescale for reasons of economy.

This invention has been especially developed to enable iron aluminumalloys to be prepared in' an air ambient" and at ordinary atmosphericpressure without sacrifice of ductility.

We have discovered that iron aluminum alloyshaving commerciallyacceptable ductilitymaybe prepared without resort to vacuum meltingprocedures provided that all' containing a very low percentage ofoxygen-and molten alloy is poured in a manner to'retaih thislow oxygencontent.

The requisite low oxygen content in the final alloy is best obtained bycombining thoroughly deoxidized iron and similarly thoroughly deoxidizedaluminum. These metals in their molten state are satisfactorilydeoxidized by treating them with a metal having an afiinity for oxygengreater than aluminum and preferably having an aflinity for this elementof the same order as calcium. By establishing in solution in the ironbath and the aluminum bath a small but significant residue of such anoxygen hungry metal, satisfactory deoxidization is assured. In this waythe final alloy bath is prepared in which aluminum oxide issubstantially absent.

In the preparation of this alloy, electrolytic iron is melted in arammed magnesia crucible without the benefit of any slag covering. Whilenot so limited, it is preferred that this melting be accomplished by useof high frequency currents. While the electrolytic iron is being melted,a bath of molten aluminum is prepared in an ordinary teapot graphitecrucible. This aluminum is held at a temperature of about 1800 F.

After melting of the electrolytic iron is complete, a preliminarydeoxidation is efiected by the addition of 0.1% aluminum and 0.5%manganese, both being added as pure metals or as ferroalloys. A moredrastic deoxidation of the molten iron is now required. This isaccomplished by exposing the melt to metallic calcium. This 2,804,387Patented Aug. 27,. 1957 ice may best be done by wiring small cubes'o'fmetallic cal:

cium to an iron rod and thrusting the iron rod intothe melt. Calcium ispreferred but for this purpose it may be replaced by an aluminum calciumalloy" or by magne; sium or any suitable combination of these elementsThe violent ebullitionof gas from the deoxidizing metal serves to purgeand violently agitateithebathi Byway ofexample, a total of 0.5% ofcalcium-is'added to-the molten" The secondof the two stages ried outjust before the mixing of the iron and aluminum iron in two stages.

so that a slight excess of calcium remains in the melt. V

In a manner similar to that described for rue-imathe aluminum is nowdeoxidized using approximately- 0.-'1;% calcium, based upon the amountof the aluminum. This. deoxidized aluminum is then further degassed byintro ducing chlorine into the melt through a refractory tube= 1 Thischlorination serves to eliminate any hydrogen whichmay have beengenerated by the'reaction of the aluminum the aluminum and water vapor.

Some oxidation of the aluminum during the pouring operation is:inevitable. However; this aluminum oxide reacts with the fiuorspar slagagainexothermically and tends to heat the bath. Precautions should betakento avoid any toxic'effects from-the aluminum fluoride whichisgenerated at this point; It isimportant during; and after the additionof the molten aluminum that the-bath be vigorously agitated. Induction"stirring? per. se: has.- not been found inadequate for this purpose'and. resort hass been had to vigorous mechanical stirring.

One-'minute prior topouring the agitation is stopped and the power shutofii. Thispermitsthe molten slagfto;

stratify so that the bulk of the slag can'b'eremoved; Cast;

iron molds which have been given awash of a chlorinated pitchor exposed.to a carbon tetrachloride atmosphere are used to receive this metal; Itis essential that the alloy be poured into the mold promptly to preventharmfufoxidation in the crucible; The metal is poured into these washedcast iron molds at about 2900 F. The hot topping procedure must takeinto account the very deep piping encountered in this type of alloy.

Promptly upon solidification the ingots are stripped from the molds andburied in a heat-insulating medium such as vermiculite or lime. This isnecessary to prevent thermal cracking because of the poor thermalconductivity and high thermal coefiicient of expression of iron aluminumalloys.

In rolling these iron aluminum ingots it is important that the maximumtemperature of the ingots does not exceed 1800 F. to avoid excessivegrain growth. A suit able practice is to charge the ingots into anelectric furnace with the heating elements off and at a temperature of1000 F. After the ingots have reached furnace temperature the furnaceand ingots are quickly brought to 1800 F. and rolling started.

Caution must be exercised in the initial rolling passes to avoidcracking of the ingot. However, conventional rolling practices can befollowed after the first few breakdown passes. For example, 2% inchdiameter ingot can be rolled to Ms inch square bar in two reheats and atotal of six mill passes. The /8 inch square bar is subsequently rolledto /8 inch diameter rod from an initial temperature of 1400 F. and atotal of four passes. Alloys cast and rolled in this manner are sound,ductile, and relatively free from surface defects.

All fiuorspar used in thisprocess should be rigidly anhydrous to avoidreaction between In the table reproduced below is shown the comparisonof metal produced according to the above outlined procedure and thatproduced by the most carefully executed vacuum melting process. I

1 Actual composition.

The preceding described procedure for producing adeoxidized alloy is byno means intended to limit the breadth of this invention. It is obviousto those skilled in the artthat the correct degree of deoxidation of theiron and of the aluminum and of the iron aluminum alloy can be attainedin many ways other than the use of the specific deoxidants mentionedabove. For example, if costs could be ignored magnesium alone willsufficiently dcoxidize the iron without recourse to the use ofmanganese, silicon or calcium. Similarly other expedients may be usedfor controlling the cooling of the ingot to prevent cracking and it maybe heated for rolling in any suitable manner as long as the temperatureof 1800 F. is quickly attained and is not substantially exceeded.

For the guidance of those who care to pursue this matter further thefollowing references are made of record.

1. E. R. Morgan, and V. F. Zackay, Ductile Iron-Aluminum Alloys, MetalProgress, vol. 61*, No. 10,1955.

2. C. Sykes, and I. W. Bampfylde, The Physical Properties ofIron-Aluminum Alloys, Iour. Iron and Steel Institute, 130, pp. 389418,1935. p j

3. I. F. Nachman, and W. J. Beuhler, 16 Percent Aluminum-Iron AlloyCold-Rolled in the Order-Disorder Range, Jour. of Applied Physics, vol.25, pp. 307 313, 1954.

4. D. C. Hilty, and W. Crafts, The Solubility of Oxygen in Liquid IronContaining Aluminum, Trans. AIME, vol. 188, p. 414, 1950.

We claim as our invention: 1 v

1. The process of producing a ductile iron aluminum alloy comprisingproducing, a bath of molten iron containing a concentration of oxygennotsubstantially higher than that concentration which corresponds to theequilibrium between calcium and oxygen at the temperature of the molteniron, producing a substantially hydrogen free bath of molten aluminumcontaining a concentration of oxygen not substantially higher. than thatconcentration,

which corresponds to the equilibrium between calcium and oxygen at thetemperature of the molten aluminum,

- establishingon the molten iron bath a layer of fluoride M03 cmomoccontaining anhydrous flux, adding the molten aluminum to the molteniron, intensively agitating the mix and promptly pouring the mixtureinto a mold.

2. The process of producing a ductile iron aluminum alloy comprisingproducing a bath of molten iron containing a concentration of oxygennotsubstantially higher than that concentration which corresponds to theequilibrium between calcium and oxygen at the temperature of the molteniron, producing a substantially hydrogen free bath of molten aluminumcontaining a concentration of oxygen not substantially higher than, thatconcentra-- tion which corresponds to the equilibrium between calciumand oxygen at the temperature of molten aluminum, establishing on themolten iron bath a layer of I fluoride containing anhydrous flux, addingthe molten alumiuum to the molten iron in an amount sufficient toproduce a alloy containing six to eighteen percent aluminum,

corresponds to the equilibrium between calcium and oxygen at the meltingpoint of the alloy.

References Cited in the file of this patent V UNITED STATES. PATENTS2,204,585 Gagnebin June 18, 1940 i FOREIGN PATENTS 440,984 Great BritainMar. 1, 1934 OTHER REFERENCES Aluminum in Iron and Steel, pages 337 and33 8. Edited by Case and Van Horn. Published in 1953 by John Wiley andSons, N. Y.

1. THE PROCESS OF PRODUCING A DUCTILE IRON ALUMINUM ALLOY COMPRISINGPRODUCING A BATH OF MOLTEN IRON CONTAINING A CONCENTRATION OF OXYGEN NOTSUBSTANTIALLY HIGHER THAN THAT CONCENTRATION WHICH CORRESPONDS TO THEEQUILIBRIUM BETWEEN CALCIUM AND OXYGEN AT THE TEMPERATURE OF THE MOLTENIRON, PRODUCING A SUBSTANTIALLY HYDROGEN FREE BATH OF MOLTEN ALUMINUMCONTAINING A CONCENTRATION OF OXYGEN NOT SUBSTANTIALLY HIGHER THAN THATCONCENTRATION WHICH CORRESPONDS TO THE EQUILIBRIUM BETWEEN CALCIUM ANDOXYGEN AT THE TEMPERATURE OF THE MOLTEN ALUMINUM, ESTABLISHING ON THEMOLTEN IRON BATH A LAYER OF FLUORIDE CONTAINING ANHYDROUS FLUX, ADDINGTHE MOLTEN ALUMINUM TO THE MOLTEN IRON, INTENSIVELY AGITATION THE MIXAND PROMPTLY POURING THE MIXTURE INTO A MOLD.